Pneumatically controlled multifunction medical ventilator

ABSTRACT

A multiple functionality pneumatically controlled medical ventilator provides precision regulation of tidal/forced breathing, and continuous positive airway pressure (CPAP)-based spontaneous breathing capability. The ventilator includes a patient breathing gas coupler that is adapted to be coupled to a patient airway breathing interface, and an input port to which a pressurized breathing gas is coupled, A pressure regulator supplies breathing gas at a positive pressure sufficiently higher than nominal lung pressure to prevent collapse of the patient&#39;s lungs. A tidal breathing gas supply unit periodically generates a volume-regulated tidal breathing gas for application to the patient airway breathing interface, while the CPAP valve supplies a pressure-regulated breathing gas to the patient airway breathing interface, in response to a patient demand for breathing gas that is exclusive of the tidal breathing supply.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of U.S. Provisional PatentApplication Serial No. 60/060,187, filed Sep. 26, 1997, entitled:“Portable Medical Ventilator,” the disclosure of which is incorporatedherein.

FIELD OF THE INVENTION

The present invention relates in general to an assisted breathing deviceor medical ventilator that may be used in a variety of human and animalpatient applications, such as, but not limited to, medical facilities(e.g., hospitals, physicians′ and veterinary offices and the like), aswell as medical field unit and emergency vehicle applications. Theinvention is particularly directed to a new and improved portablemedical ventilator that provides both precision pneumatic regulation oftidal/forced breathing, and continuous positive airway pressure(CPAP)-based spontaneous breathing capability.

BACKGROUND OF THE INVENTION

Currently available portable medical ventilator units generally fallinto one of two categories: i- relatively simple or limited capabilitypneumatically controlled units (typically carried by emergencyvehicles), and ii-sophisticated electrically (both AC and battery)powered, electronically (microprocessor)-controlled systems, that areessentially comparable in function to in-house (e.g., hospital) devices.The former devices suffer from the fact that they are not much more thatemergency oxygen supplies. An obvious drawback to the devices of thesecond category is the fact that, as electrically powered, system levelpieces of equipment, they are relatively expensive and complex.Moreover, electronic systems are subject to a number of adverseinfluences, such as electromagnetic interference, handling abuse, andbattery life-factors which do not affect a pneumatic system.

SUMMARY OF THE INVENTION

In accordance with the present invention, drawbacks of conventionalmedical ventilator devices such as those described above are effectivelyobviated by a new and improved portable, pneumatically controlledmedical ventilator that provides the multiple functionality of anelectronically controlled ventilator, but without the need for anyelectrical power (including batteries), thereby making the unitespecially suited for field and emergency vehicle applications.

For this purpose, the pneumatically controlled medical ventilator of thepresent invention has an input port coupled to a source of pressurizedgas, such as an oxygen tank carried by a medical emergency vehicle. Apneumatic link from the input port is coupled to a system-priming gasflow control switch, which is operative to prime a pneumatic timingcartridge within a pneumatic timing unit, when the ventilator isinitially coupled to the oxygen source. The input port is furthercoupled to a system gas flow pressure regulator. The output of thesystem gas flow pressure regulator is coupled to an input port of atidal breathing control switch, the operation of which controls the flowof mandatory tidal breathing gas to the patient.

The system gas flow pressure regulator provides a prescribed elevated orpositive driving pressure for the mandatory tidal breathing gas supplysubsystem, so that a precisely regulated amount of breathing gas may becontrollably supplied to the patient. This constant positive pressure isconsiderably higher than the nominal lung pressure of a patient, so thatit is effective to prevent collapse of the patient's lungs, and is notaffected by changes in the patient's lung compliance and resistance.

The filtered breathing gas supplied is further coupled to a continuouspositive airway pressure (CPAP) valve. The CPAP valve has a sensing orcontrol port coupled to the breathing gas supply throat of a patient airsupply output coupler for sensing a drop in pressure when the patientinitiates or demands a breath, separate from a mandatory tidal breathingcycle. A section of breathing gas supply tubing is coupled between thepatient air supply output coupler and an airway breathing interface onthe patient. In response to the patient spontaneously drawing a breath,the drop in pressure in the breathing gas supply throat of the outputcoupler will cause the CPAP valve to couple the breathing gas (oxygen)to a gated venturi unit installed at an upstream end of the patient airsupply output coupler. The venturi unit includes an ambient air inputport through which filtered ambient air is drawn into the patient airsupply output coupler by the flow of pressurized oxygen supplied toinput port, and thereby allow a prescribed spontaneous or on-demandoxygen-enriched breathing mixture to be supplied to the patient.

An auxiliary anti-suffocation valve is coupled to the main airflowpassageway of the patient air supply output coupler, to ensure thatambient air can be drawn into the main airflow passageway and suppliedto the patient, in the event of a ventilator failure or depressurizationof the oxygen source. Also, an overpressure valve is coupled to the mainairflow passageway of the patient air supply output coupler, to preventan excess pressure build up within the main airflow passageway of thecoupler, and within the patient's lungs.

The presetable gas pressure provided at the output port of the CPAPvalve is further coupled to a pneumatic conduit for inflating thediaphragm of an exhalation valve of an airway breathing interface on thepatient. When a breath drawn in by the patient is patient-initiated, thepressured gas supplied by CPAP valve to the exhalation valve outletinflates the exhalation valve's diaphragm and prevents the breathing gasin the tubing breathing gas tubing from being exhausted from theexhalation valve, and instead directed into the patient's airway, asintended. When the patient ceases inhaling, there is no longer apressure drop in the coupler throat, causing the CPAP valve to close,and interrupt the positive pressure at the exhalation valve outlet. Theexhalation valve's diaphragm thereby deflates to allow the patient toexhale.

The pneumatic timing unit supplies a periodic pneumatic control signalassociated with a controllable (oxygen) concentration and rate of tidalbreathing gas to a normally closed tidal breathing control switch. Tidalbreathing parameters of the pneumatic control signal supplied to thepneumatic timing unit includes a pneumatic timing cartridge and apneumatic time constant circuit for controlling the charge and bleedrates of the pressurized gas. The tidal breathing control switchreceives the pressure-regulated oxygen from the system pressureregulator, and outputs a pressure-regulated oxygen to a dual positiontidal air supply-mixture switch.

For a first position, the tidal air supply-mixture switch couples thepressure-regulated oxygen from the tidal breathing pneumatic circuitryto an oxygen concentration-reducing venturi, that is coupled to theoutput throat of the patient air supply coupler. To supply a pure (100%)oxygen breathing gas to the patient's airway breathing interface, thetidal air supply-mixture switch is turned, and thereby ported to a 100%oxygen outlet port, which is coupled through a section of oxygen supplytubing to a pure oxygen feed input port of the patient's airwaybreathing interface.

A manually setable, pressure regulator valve is coupled to the tidalbreathing supply, and is operative to feed the exhalation valve outlet.As with the operation of the CPAP valve for an on-demand breath, thisserves to inflate the exhalation valve's diaphragm, and prevent thebreathing gas from being exhausted from the exhalation valve, butdirected instead into the patient's airway. At the end of the tidalbreath interval, the positive pressure at the output of the tidalbreathing control switch is interrupted, terminating the positivepressure at the output of the pressure limit regulator valve necessaryfor inflating the diaphragm of the exhalation valve. The exhalationvalves diaphragm deflates to allow the patient to exhale.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 diagrammatically illustrates the architecture of the medicalventilator of the present invention; and

FIG. 2 diagrammatically illustrates a patient airway breathing interfaceto which the medical ventilator of FIG. 1 may be coupled.

DETAILED DESCRIPTION

Before describing in detail the pneumatically controlled multifunctionmedical ventilator of the present invention, it should be observed thatthe invention resides primarily in what is effectively a prescribedcombination of conventional pneumatic flow control and pressureregulation devices and components and interconnections therefor. As aresult, for the most part, the configurations of such devices andcomponents, and the manner in which they are interfaced withconventional breathing equipment have been illustrated in the drawingsin readily understandable pneumatic flow control circuit block diagramform, which show only those specific details that are pertinent to thepresent invention, so as not to obscure the disclosure with detailswhich will be readily apparent to those skilled in the art having thebenefit of the description herein. Thus, the pneumatic block diagramillustrations are primarily intended to show the major components of theventilator system in a convenient functional grouping and flow controlarrangement, whereby the present invention may be more readilyunderstood.

Referring now to FIG. 1, the architecture of the pneumaticallycontrolled medical ventilator of the present invention isdiagrammatically illustrated as comprising a patient breathing gas(oxygen) inlet port 10, to which a pressurized (e.g., within a range of40-100 psi) source of a prescribed breathing gas (e.g., oxygen) 11 iscoupled. This pressurized breathing gas source (such as a pressurizedoxygen tank carried by a medical emergency vehicle) serves as a sourceof both (periodically metered) tidal and patient on-demand breathing gasfor the patient, and to operate as a pneumatic supply for controllingthe operation of the various components of the ventilator. By basing theoperation of the ventilator exclusively upon mechanically andpneumatically driven components, without any need for electrical orelectronic circuits, the ventilator of the invention is readily suitedfor the typical limited or no notice need of emergency medical personneland eliminates any concern for the availability and or operability ofbatteries. All medical personnel require is a source of breathing gas(e.g., an oxygen gas tank).

A pneumatic link 12 from input port 10 is coupled directly through aflow-reducing orifice 13 to the flow control or signal input port 101 ofa normally open (system-priming) gas flow control switch 100, such as anIndustrial Specialties Model No. AVAP2-1032NOM. Because it is normallyopen, the gas flow control switch 100 provides a gas flow path forpressurized gas from the gas supply source 11 that enables a pneumatictiming cartridge 200 within a pneumatic timing unit 110, to bedescribed, to be immediately pressurized when the ventilator is firstconnected to the breathing gas supply.

The pneumatic link 13 from the gas input port 10 is further coupledthrough an air filter 14 to a pneumatic link 15, that is coupled to aninput port 21 of a system gas flow pressure regulator 20 (such as aNorgen Model No. R07-100NKA regulator, as a non-limiting example). Theoutput port 22 of the system gas flow pressure regulator 20 is coupledthrough a pneumatic supply link 99 to the control port 102 of the gasflow control switch 100 and to the input port 201 of the pneumatictiming cartridge 200. It is also coupled to an input port 121 of anormally closed tidal breathing control switch 120, the operation ofwhich controls the flow of mandatory tidal breathing gas to the patient,as will be described.

The system gas flow pressure regulator 20 serves to provide a prescribedpositive driving pressure for the mandatory tidal breathing gas supplysubsystem, whereby a precisely regulated amount of breathing gas may becontrollably and repetitively supplied at a prescribed rate and volumeto the patient. Regardless of the breathing volume of the patient (whichmay typically vary from 120 to 1,500 milliliters per breath) the tidalvolume settings do not change.

As will be described, the oxygen content of the tidal breathing gas maybe varied between pure or 100% oxygen and a relatively reduced oxygenpercentage (e.g., on the order e of 60%). This constant positivepressure (e.g., on the order of 30 psi) is considerably higher than thenominal lung pressure of a patient (which is zero psi), so that it iseffective to prevent collapse of the patient's lungs a not uncommoncondition in ill or injured patients.

The pneumatic link 15 is further coupled to a manually adjustable lowpressure alarm switch 40 (such as a Pisco Model No. RPV-⅛-10-32 F unit),the output 41 of which is coupled through a flow orifice 42 to an alarmdevice, such as a pneumatic whistle 44, which is activated if the inputgas pressure drops below a prescribed minimum value. The filteredbreathing gas supplied over the pneumatic link 15 is further coupled toan input port 31 of a continuous positive airway pressure (CPAP) valve30, such as a Bird Products Model No. 4715 valve, as a non-limitingexample. The CPAP valve 30 is operative to maintain a continuouspositive pressure regardless of the patient's effort to breath. CPAPvalve 30 has a patient demand pressure-monitoring or control port 32,that is coupled through a manually adjustable damping orifice 52 to apatient air supply-monitoring pneumatic link 50. Pneumatic link 50 iscoupled to an on-demand breath monitoring port 61, which is coupled tothe breathing gas supply throat 62 of a patient air supply outputcoupler 60.

To allow the pressure in the patient airway to be visually monitored byattendant medical personnel, the pneumatic link 50 is also coupledthrough a flow orifice 54 to an airway-monitoring pressure gauge 56. Asection of hose or tubing 70 is coupled between the patient air supplyoutput coupler 60, and an airway breathing interface on the patient,diagrammatically illustrated at 68 in FIG. 2. In addition, link 50 maybe coupled to an external sensor (not shown) of an unobtrusive off-linemicrocontroller-based monitoring system, for monitoring the operation ofthe system by supervisory medical (e.g., hospital) personnel.

By ‘on-demand’ is meant a breath that is drawn by the patient, inaddition to the ‘mandatory’ tidal breathing breath periodically suppliedby the pneumatic timing unit 110. As a non-limiting example, thisauxiliary source of breathing gas is particularly useful where medicaltreatment involves ‘weaning’ the patient off the tidal breathing supply,by gradually reducing the number of tidal breaths supplied per minute,and forcing the patient to begin to initiate more breathing on his own.

For this purpose, in response to the patient spontaneously drawing abreath (at a time other than at the occurrence of the periodic supply ofa prescribed quantity of tidal breathing gas), there will be a drop inpressure in the breathing gas supply throat 62 of the output coupler 60.This drop in pressure will be coupled by the pneumatic link 50 to thepatient demand pressure-monitoring port 32 of the CPAP valve 30, causingthat valve to open and couple the breathing gas (oxygen) in thepressurized gas link 15 to its output port 33, at a prescribed pressure,manually setable by a valve control knob 36.

The presetable gas pressure provided at the output port 33 of the CPAPvalve 30 is coupled through a pneumatic link 72 and an adjustableproportioning orifice 73 to a pneumatic conduit 75 for inflating thediaphragm of an exhalation valve 106 of the patient airway breathinginterface 68 of FIG. 2. CPAP output port 33 is further coupled over link72 to an input port 74 of a gated venturi unit 76 installed at anupstream end of the patient air supply output coupler 60. As anon-limiting example, the gated venturi unit 76 may comprise a venturiunit available from Bird Products, referenced above.

The gated venturi 76 includes an ambient air input port 78 in which anair filter 82 is installed. It is through the venturi's air input port78 that filtered ambient air is drawn into the patient air supply outputcoupler 60 by the flow of pressurized oxygen supplied to input port 74,to allow a prescribed spontaneous or on-demand oxygen-enriched breathingmixture to be supplied to the patient. For this purpose, the output ofthe gate venturi 76 is coupled (through an overpressure valve 88) intothe main airflow passageway 64 of the patient air supply output coupler60, so that a prescribed mixture of pure oxygen supplied from CPAP valve30 and ambient air, as drawn into the venturi 76, is coupled into thethroat 62 of the patient air supply output coupler 60 for delivery tothe patient airway breathing interface 68.

An auxiliary anti-suffocation valve 86 (such as a Bird Product's ModelNo. 5536, as a non-limiting example) is coupled to the main airflowpassageway 64 of the patient air supply output coupler 60. Thisauxiliary valve ensures that ambient air can be drawn into the mainairflow passageway and supplied to the patient, in the event of afailure or depressurization of the oxygen source. As long as a positiveair/oxygen flow for the patient is provided in the main airflowpassageway 64 of the coupler, the anti-suffocation valve 86 remainsclosed, so that the air supply to the patient is controlled by thedemand or tidal pneumatic control components of the invention. Anoverpressure or pressure limit valve 88 (such as a Halkey-Roberts ModelNo. 780 RPA 125, as a non-limiting example) is coupled to the mainairflow passageway 64 of the patient air supply output coupler 60, toprevent an excess breathing mixture pressure build up within the mainairflow passageway of the coupler 64.

As pointed out above, the output port 33 of the CPAP valve 30 is coupledthrough a pneumatic link 72 and a proportioning (pressure reduction)orifice 73 to pneumatic conduit 75 for inflating the diaphragm ofexhalation valve 106 of patient airway breathing interface 68. For thispurpose, the conduit 75 is coupled through an orifice 91 to anexhalation valve outlet 93. It is also ported to the atmosphere via acoupling orifice 97 and an air filter 98. The exhalation valve outlet 93is coupled to a section of tubing 95 that is ported to a diaphragminflation control port 104 of an exhalation valve 106 of the patient'sbreathing interface 68.

When a breath drawn in by the patient is a patient-initiated(spontaneous or on-demand) breath, to which the CPAP valve 30 respondsin the manner described above, the pressured gas supplied by CPAP valve30 (through conduit 75) to the exhalation valve outlet 93 inflates theexhalation valve's diaphragm and prevents the breathing gas in thetubing 70 from being exhausted via the output port 108 of exhalationvalve 106, and instead directed into the patient's airway, as intended.When the patient ceases inhaling, there is no longer a pressure drop inthe coupler throat 62 and link 50, causing the CPAP valve 30 to close.This interrupts the positive pressure at the exhalation valve outlet 93necessary for inflating the diaphragm of the exhalation valve 106. Thediaphragm thereby deflates to allow the patient to exhale though theexhalation valve.

As described briefly above, the pneumatic timing unit 110 serves togenerate a periodic pneumatic control signal associated with acontrollable (oxygen) concentration and rate (e.g., in a range of fromtwo to sixty breaths per minute) of tidal breathing gas. This tidalbreathing pneumatic control signal is supplied via a pneumatic link 119to a control port 122 of the normally closed tidal breathing controlswitch 120. (As a non-limiting example, tidal breathing control switchflow 120 may comprise a Decker Model No. 1003 flow switch.) As pointedout above, the input port 121 of the tidal breathing control switch 120is coupled to receive the pressure-regulated oxygen supplied viapneumatic link 99 from the system pressure regulator 20. Switch 120 hasan output port 123 through which the pressure-regulated oxygen flow inpneumatic link 99 is periodically coupled to a tidal breathing supplypneumatic link 125.

The tidal breathing supply pneumatic link 125 is coupled to an inputport 131 of a dual position tidal air supply-mixture switch 130, such asa Norgren Model No. 5CV-022-000 air mix switch, as a non-limitingexample. The tidal air supply-mixture switch 130 has a first output port132 coupled to a first, pressurized oxygen input port 141 of a tidaloxygen/air mixture feed venturi 140, such as a Festo Model No. 9394venturi, as a non-limiting example. The venturi 140 is controllablycoupled in the breathing gas supply path to the patient when the oxygenconcentration of the breathing gas is to be less than 100% (pure O₂).e.g., on the order of 60%, as a non-limiting example. For this purpose,venturi 140 has an output port 143 coupled to a tidal gas mixture feedport 65 installed in the output throat of the patient air supply coupler60. The pneumatic signal input at control port 122 is reduced inpressure by an orifice 148 and enters the tidal mixture feed port 65 ofthe patient air supply coupler 60. This link serves to exhaust the gassignal delivered to control port 122. It may be noted that with thepressure (e.g., 35 psi) at control port 122 being higher than thepressure at tidal mixture feed port 65 (e.g., less than or equal to 1psi), gas always flows from port 122 to port 65.

Venturi 140 has a second, ambient air input port 144 coupled through acheck valve 145 and a filter 146. As in the gated venturi 76 employedfor on-demand breathing, ambient air for a reduced oxygen concentrationtidal breathing mixture supplied to tidal mixture feed port 65 of thepatient air supply coupler 60 is drawn into the input port 144 ofventuri 140 by the flow of pressurized oxygen supplied to the venturi'sinput port 141, so as to provide a prescribed oxygen-enriched tidalbreathing air mixture to the patient.

In order to supply pure (100%) oxygen breathing gas to the patient'sairway breathing interface 68 (associated with a 90° clockwise rotationof the valve relative to that shown in FIG. 1), the tidal airsupply-mixture switch 130 has a second output port 133 coupled throughan oxygen feed orifice 135 to a 100% oxygen outlet port 136. The pureoxygen outlet port 136 is coupled through a section of oxygen supplytubing 138 to a pure oxygen feed input port 107 of the patient's airwaybreathing interface 68.

A manually setable, pressure regulator valve 150 (such as an AirtrolModel No. R-900-10-W/S) has a pressure input port 151 coupled to thetidal breathing supply pneumatic link 125. An output port 152 ofpressure regulator valve 150 is coupled through a check valve 154 topneumatic supply conduit 75, that feeds the exhalation valve outlet 93.The pressure limit regulator valve 150 is operative to supply aprescribed level of exhalation valve pressurizing gas to the exhalationvalve outlet 93 during a tidal breathing interval, which preventsexcessive pressure build-up in the patient's lungs.

As pointed out previously, this serves to inflate the exhalation valve'sdiaphragm, and thereby prevents the breathing gas in the tubing 70 frombeing exhausted from the exhalation valve 106, but directed instead intothe patient's airway, as intended. At the end of the tidal breathinterval, the positive pressure at the output 123 of the tidal breathingcontrol switch 120 is interrupted, thereby terminating the positivepressure in link 125 and at the output port 152 of pressure limitregulator valve 150 necessary for inflating the diaphragm of theexhalation valve 106. The exhalation valves diaphragm thereby deflatesto allow the patient to exhale.

In order to define the (volume and timing) parameters of the tidalbreathing control signal supplied to the control input 121 of the tidalbreathing control switch 120, the input port 201 of the pneumatic timingcartridge 200 (such as Bird Products Model No. 6830 pneumatic timingcartridge, as a non-limiting example) of the pneumatic timing unit 110is coupled to the pressure-regulated oxygen flow pneumatic link 99. Port201 is used to continuously pressurize the timing cartridge 200 duringrepetitive tidal breathing cycles, subsequent to the initial charging ofthe pneumatic timing cartridge 200 via a control port 202 that iscoupled to the output port 103 of the normally open gas flow controlswitch 100, as described above.

The pneumatic timing cartridge 200 has an output port 203 coupled to thepneumatic link 119, and through a check valve 211 to a variablepneumatic resistor element 213, and through a check valve 215 to apneumatic timing circuit 220. The pneumatic timing circuit 220 includesa volume balance orifice 221 and a pneumatic flow time constant controlpath 222, that is comprised of a variable pneumatic resistor element 224and a variable pneumatic capacitor element 226, which is charged by theoutput 203 of the pneumatic timing cartridge 200. A check valve 228 iscoupled between the pneumatic timing circuit 220 and the variablepneumatic resistance element 213. The variable pneumatic resistor 213provides a pressure bleed path to ambient air through an airfilter/muffler 230. The tidal breathing rate and the duty cycle of arespective tidal breath interval are preset by the time constantparameters of the components of the pneumatic timing circuit 220.

In operation, regulated pressure gas enters the input port 201 of thepneumatic timing cartridge 200. Since the timing cartridge 200 isnormally open, the gas immediately exits to both the flow control switch120 and through the check valves 211 and 215 to the pneumatic timingcircuit 220. As the gas flows through the timing circuit it flowsthrough the variable resistors 224 and 221 and variable capacitor 226and begins to meter into timing cartridge 200. As described above, theparameters of the pneumatic resistor and capacitor components of thetiming circuit may be set to provide a controllable breathing rate in arange of from two to sixty breaths per minute. At the same time, thisgas pressure is delivered downstream of check valve 228 through ratecontrol variable resistor 213. Since the volume of gas transferred bythe high pressure cannot escape through the rate control path fastenough (the orifice is essentially saturated), the high pressure ismaintained against the check valve 228, holding it closed.

With check valve 228 held closed, absent leaks, gas entering port 202 ofthe timing cartridge 200 by way of the volume control components cannotescape. As a consequence, the pressure inside the ‘sealed’ timingchamber increases at a rate determined by the settings of the volumecontrol variable resistors 224 and 221. The pressure continues to rise,until it reaches that required to turn off the timing cartridge 200(e.g., between 10 and 15 psi). When the gas flow is terminated, the gasexits from the timing chamber 200 through the check valve 228 and therate control variable resistor 213 and air filter/muffler 230 of therate control path. Once the pressure drops low enough in its timingchamber, the timing cartridge 200 turns back on.

As will be appreciated from the foregoing description, drawbacks ofconventional medical ventilator devices described above are effectivelyobviated by the exclusively pneumatically controlled medical ventilatorof the invention. By means of a dual, regulated positive pressure,tidal/on-demand breathing gas supply architecture, that requires noelectrical power (including batteries), the invention is especiallysuited for a variety of hospital, field and emergency vehicleapplications.

While I have shown and described an embodiment in accordance with thepresent invention, it is to be understood that the same is not limitedthereto but is susceptible to numerous changes and modifications as areknown to a person skilled in the art, and I therefore do not wish to belimited to the details shown and described herein, but intend to coverall such changes and modifications as are obvious to one of ordinaryskill in the art.

What is claimed is:
 1. A pneumatically controlled medical ventilatorapparatus comprising: a patient air supply output coupler that isconfigured to be coupled to a patient airway breathing interface; abreathing gas input port to which a pressurized supply of breathing gasis coupled; a tidal breathing gas supply unit coupled to said breathinggas input port, and being operative to periodically supply acontrollable concentration of regulated volume tidal breathing gas forapplication to said patient airway breathing interface; and a continuouspositive airway pressure (CPAP) valve including a valve input port and apatient demand monitoring port, the valve input port being coupled tothe breathing gas input port, and said CPAP valve being operative tosupply regulated pressure breathing gas to said patient air supplyoutput coupler, in response to a patient initiating a breath; saidpatient air supply output coupler including a venturi unit and anon-demand breath monitoring port connected to the patient demandmonitoring port of said CPAP valve, the venturi unit also being coupledto a source of ambient air, and being operative to supply said regulatedpressure breathing gas as a mixture of ambient air and said pressurizedbreathing gas.
 2. A pneumatically controlled medical ventilatorapparatus according to claim 1, wherein said CPAP valve has a controlport coupled to said patient air supply output coupler, and beingoperative to supply said regulated pressure breathing gas in response toa prescribed change in pressure of said control port.
 3. A pneumaticallycontrolled medical ventilator apparatus according to claim 1, whereinsaid tidal breathing gas supply unit is operative to periodically supplya controllable concentration of tidal breathing gas to said patient airsupply output coupler.
 4. A pneumatically controlled medical ventilatorapparatus according to claim 3, wherein said tidal breathing gas supplyunit includes a venturi unit coupled to a source of ambient air and to aperiodically supplied quantity of regulated pressure breathing gas, andbeing operative to supply said controllable concentration of regulatedpressure breathing gas as a mixture of ambient air and said regulatedpressure breathing gas to said patient air supply output coupler.
 5. Apneumatically controlled medical ventilator apparatus according to claim1, wherein said tidal breathing gas supply unit is configured toperiodically supply a first concentration of tidal breathing gas to saidpatient airway breathing interface.
 6. A pneumatically controlledmedical ventilator apparatus according to claim 5, wherein said tidalbreathing gas supply unit is configured to periodically supply a secondconcentration of tidal breathing gas to said patient air supply outputcoupler.
 7. A pneumatically controlled medical ventilator apparatusaccording to claim 1, wherein said patient airway breathing interfaceincludes an exhalation valve, and wherein each of said tidal breathinggas supply unit and said CPAP valve is coupled to provide a regulatedpressure for controlling the operation of said exhalation valve.
 8. Apneumatically controlled medical ventilator apparatus according to claim1, wherein said tidal breathing gas supply unit comprises a pneumatictiming unit and a tidal breathing control switch, said pneumatic timingunit being operative to supply a periodic pneumatic control signalassociated with a prescribed supply of tidal breathing gas to the tidalbreathing control switch, said tidal breathing control switch beingoperative to controllably couple pressure-regulated breathing gas tosaid patient airway breathing interface.
 9. A pneumatically controlledmedical ventilator apparatus according to claim 8, wherein saidpneumatic timing unit includes a pneumatic timing device and a pneumatictime constant circuit coupled therewith for controlling charging andbleeding of pressurized gas with respect to said pneumatic timingdevice, and thereby defining a tidal breathing rate and a duty cycle ofa respective tidal breath interval of a periodically suppliedcontrollable concentration of regulated volume tidal breathing gasapplied to said patient airway breathing interface.
 10. A pneumaticallycontrolled medical ventilator apparatus comprising a patient breathinggas output adapted to be coupled to a patient airway breathing interfaceapplied to a patient, a breathing gas input port to which a pressurizedbreathing gas is coupled, a gas pressure regulator coupled to saidbreathing gas input port, and being operative to supply said breathinggas at a prescribed positive pressure higher than the nominal lungpressure of said patient, that is effective to prevent collapse of thepatient's lungs, a tidal breathing gas supply unit coupled to said gaspressure regulator, and being operative to periodically generate avolume-regulated tidal breathing gas for application to said patientairway breathing interface, and a continuous positive airway pressure(CPAP) valve including a valve input port and a patient demandmonitoring port, the valve input port being coupled to the breathing gasinput port, and said CPAP valve being operative to supplypressure-regulated breathing gas to said patient breathing gas output inresponse to a patient demand for breathing gas, said patient breathinggas output including a venturi unit and an on-demand breath monitoringport connected to the patient demand monitoring port of said CPAP valve,the venturi unit also being coupled to a source of ambient air, and isoperative to supply said regulated pressure breathing gas as a mixtureof said ambient air and said pressurized breathing gas in response to aprescribed change in pressure of said patient demand monitoring port.11. A pneumatically controlled medical ventilator apparatus according toclaim 10, wherein said tidal breathing gas supply unit is operative toperiodically supply a first concentration of tidal breathing gas to saidpatient airway breathing interface, and a reduced concentration of tidalbreathing gas to said patient breathing gas output.
 12. A pneumaticallycontrolled medical ventilator apparatus according to claim 11, whereinsaid tidal breathing gas supply unit includes a venturi unit coupled toa source of ambient air and to a periodically supplied quantity ofpressure-regulated breathing gas, and being operative to supply saidreduced controllable concentration of breathing gas as a mixture of saidambient air and said pressure-regulated breathing gas to said patientbreathing gas output.
 13. A pneumatically controlled medical ventilatorapparatus according to claim 10, wherein said patient airway breathinginterface includes an exhalation valve, and wherein each of said tidalbreathing gas supply unit and said CPAP valve is coupled to provide aregulated pressure for controlling the operation of said exhalationvalve.
 14. A pneumatically controlled medical ventilator apparatusaccording to claim 10, wherein said tidal breathing gas supply unitcomprises a pneumatic timing unit and a tidal breathing control switch,said pneumatic timing unit being operative to supply a periodicpneumatic control signal associated with a prescribed supply of tidalbreathing gas to the tidal breathing control switch, said tidalbreathing control switch being operative to controllably couplepressure-regulated breathing gas to said patient airway breathinginterface.
 15. A method of providing a patient breathing gas to apatient airway breathing interface of a patient, comprising the stepsof: (a) periodically pneumatically supplying a regulated pressurebreathing gas, at a positive pressure higher than the nominal lungpressure of said patient and effective to prevent collapse of thepatient's lungs, to said patient airway breathing interface; and (b) inresponse to a pneumatically based patient demand for breathing gas, andexclusive of said periodic pneumatic supply of a tidal breathing gas instep (a), pneumatically supplying a continuous positive airway pressure(CPAP) breathing gas to said patient airway breathing interface througha venturi unit as a mixture of ambient air and pressurized breathinggas.
 16. A method according to claim 15, wherein step (a) comprisesselectively periodically supplying one of a first concentration of tidalbreathing gas to said patient airway breathing interface, and a second,reduced concentration of tidal breathing gas to said patient airwaybreathing interface.
 17. A method according to claim 15, wherein saidpatient airway breathing interface includes an exhalation valve, andwherein each of steps (a) and (b) comprises providing a regulatedpressure for controlling the operation of said exhalation valve.